1. Field of the Invention
This invention relates to an in-wheel motor provided in a wheel rim of a vehicle to drive a driving wheel to rotate.
2. Description of the Related Art
The in-wheel motor provided in a wheel rim of a vehicle to directly drive a driving wheel is used widely, particularly in relatively small-size vehicles such as forklifts and golf carts, since it provides various advantages such that the space required in a vehicle body can be reduced, that a transmission and a differential gear unit can be omitted, and that a drive shaft can be omitted when an independent suspension is adopted. Various structures are known for this type of in-wheel motor. As one example, an in-wheel motor having a stator and a rotor arranged like a double ring is proposed, for example, in Japanese Unexamined Patent Publication No. 2004-161189 (referred to as “Patent Document 1”).
To incorporate the in-wheel motor disclosed in Patent Document 1, a common suspension structure, in which a wheel is rotatably fitted to a knuckle of a suspension of a vehicle by means of a hub unit, is adopted. An annular stator is floatingly supported over the knuckle by means of buffer members, and an annular rotor is rotatably supported on the stator by means of a bearing inserted therebetween so as to be arranged outside the outer circumference of the stator. While variation of position of the rotor caused by floating support is allowed by cross guides, rotation of the rotor caused by the stator excited is transferred to the wheel.
In the in-wheel motor in Patent Document 1, since the rotor is rotatably supported on the stator by means of the bearing inserted therebetween so as to be arranged outside the outer circumference of the stator, the bearing is at a great distance from the axis of rotation of the hub unit. Hence, circumferential velocity around the bearing is very high, which causes durability of the bearing, and therefore, reliability of the in-wheel motor to lower.